I am not sure this is either fully accurate or if it is a good idea (for me) to attempt to redo percent coverage of body locations for clothing or armor. I will probably end up wasting a lot of time working on it and end up chucking it all anyway. I welcome mocking, insults and other input from you good folks.

The link has gone kaput. I have a PDF of the data and I would be happy to send it to anyone who asked for it as an Email attachment.

In the end , I ended with each type of armor piece describing how much it covered of each body part and at which angle (front, back, top, etc...).

When someone made a targeted attack, the GM had to roll a d100 to see which part of the bodypart was struck.

I started with this because I wanted the players to be able to buy/gather pieces of armor (e.g., a pauldron, damaged armor, different sizes of sleeved mailshirts...).

But as you state it, wasted a lot of time and discarded it in the end. Main reason was that I do everything from GCA4 and it doesn't allow me to create new hit locations (like shoulders, elbows, knees) and attack a %-value to the listed DR. And I made a promise to myself, "If I can't do it in GCA4, I won't do it at all".

I use GCA for everything equipment also. There are rules for attacks on shoulders, elbows, knees. GURPS 4th - Low-Tech - Instant Armor has it. And there are some rules for front vs back attacks, like against the skull. I think it's -7 from the Front, -5 from the Back. (as per tactical combat and facing)

I don't mind putting in the work to make a functioning rules adjustment, so long as the extra work is all contained at the front end, and it doesn't terribly increase the number crunching during play. One extra roll to determine what part of an arm was struck isn't going to bog down combat. The problem comes about when you go back and try to retro fit it into preexisting rules and stats. Like is groin independent or part of abdomen? Can it be struck with attacks from the Left, Right and Back? What does that do to calculating armor piece by piece if the front and back are different?